Wideband cable system

ABSTRACT

A wideband cable modem system increases available bandwidth of a single channel by encoding a data stream into wideband packets. The wideband packets are associated with a logical wideband channel that extends over multiple physical downstream cable channels.

BACKGROUND

The Data Over Cable Service Interface Specification (DOCSIS) standarddefines a high speed, bi-directional, data communication channel betweencable providers and cable customers. The DOCSIS standard defines thelayer 1 thru layer 3 communication protocols, timings, and RadioFrequency (RF) specifications for data traffic over cable systems. Thecommunication media can be either coaxial cable or fiber.

FIG. 1 shows how Internet Protocol (IP) traffic is currently transferredover a DOCSIS system. A communication link is established between aCable Modem Termination Systems (CMTS) 14 on the cable provider end anda Cable Modem (CM) 20 on the customer premises. Data transfers from theCMTS 14 to the CM 20 are referred to as downstream while transfers fromthe CM 20 to the CMTS 14 are referred to as upstream.

The CMTS 14 at a cable system headend may include a Wide Area Networkconnection 12, such as an Ethernet connection, that receives IP traffic.Other types of network interfaces may also be used such as DynamicPacket Transport/Resilient Packet Ring (DPT/RPR) orPacket-over-SONET/SDH (POS) The CMTS 14 modulates the IP traffic over asingle downstream channel 16 on a high speed Hybrid Fiber Coax (HFC) 19.In one instance, the single downstream channel 16 has a bandwidth limitof about 30 to 42 Million Bits Per Second (Mbps) and may supplydownstream IP connectivity for up to 8000 different cable modems 20connected to the same cable plant 19. Each cable modem 20 demodulatesthe downstream traffic and formats the traffic for transfer overEthernet link 22. Upstream IP traffic is transferred over upstreamchannel 18.

Most cable traffic consists of data flowing in the downstream directionfrom CMTS 14 to CM 20. Current bandwidth may be sufficient for largenumbers of cable modems with bursty traffic that can operate efficientlyon shared bandwidth. However, current cable systems cannot supportapplications that have a high average bandwidth such as Constant BitRate (CBR) or Variable Bit Rate (VBR) Video.

The present invention addresses this and other problems associated withthe prior art.

SUMMARY OF THE INVENTION

A wideband cable modem system increases available bandwidth of a singlechannel by encoding a data stream into wideband packets. The widebandpackets are associated with a logical wideband channel that extends overmultiple downstream physical cable channels.

The foregoing and other objects, features and advantages of theinvention will become to more readily apparent from the followingdetailed description of a preferred embodiment of the invention whichproceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a background diagram showing downstream and upstream channelused in a cable plant for transferring IP data.

FIG. 2 is a block diagram showing how a wideband cable system usesmultiple downstream channels for carrying downstream IP traffic.

FIG. 3 is a detailed diagram of the circuitry used in a wideband cablesystem.

FIG. 4 shows MPEG packet ordering in a wideband channel.

FIGS. 5-9 show different fields in a wideband packet.

FIGS. 10 and 11 show how wideband channels are dynamically changed overdifferent RF channels.

FIGS. 12-14 show how different wideband and narrowband channels areassociated with different RE channels.

FIG. 15 shows how DOCSIS MAC frames can span wideband packets.

FIG. 16 shows one example of how bytes are striped over multiple RFchannels.

FIG. 17 shows a wideband channel descriptor.

FIG. 18 is a block diagram showing how the wideband cable system isconfigured.

DETAILED DESCRIPTION

Referring to FIG. 2, a group of downstream RF channels 30 in an HFC 33are bundled together into one wideband channel 35. A single RE channel30 is defined in the nomenclature of the present invention as aNarrowBand (NB) channel. The wideband channel 35 is a logical channelthat spans one or more physical RF channels 30.

An IP server 26 outputs an IP data stream to a Wideband Cable ModemTermination System (WCMTS) 28 over an Ethernet connection 27 or someother type of Wide Area Network (WAN) link. Any type of data can be sentover connection 27, but in one example a video data stream is sent. TheWCMTS 28 transmits portions of the data stream over the multipledifferent downstream RF channels 30.

The wideband channel 35 contains a number of wideband transportsub-channels which can be dynamically adjusted for varying bandwidthrequirements. Legacy protocols can be interlaced into the widebandchannel maintaining backward compatibility with existing cable modems.The bandwidth of the wideband channel 35 provides scalable and efficientVariable Bit Rate (VBR) utilization of data/voice/video IP streams in aDOCSIS compatible environment.

The individual downstream RF channels 30 are received at one or moreWideband Cable Modems (WCMs) 34 on the HFC plant 33. In one embodiment,the WCMTS 28 also operates as a conventional CMTS 14 (FIG. 1) and theWCMs 34 also operate as conventional CMs 20 as shown in FIG. 1. Anupstream channel 32 is used for upstream DOCSIS communications from theWCMs 34 to the WCMTS 28.

The RF channels 30 are independent of each other. All RF channels 30could originate from a single multi-channel WCMTS 28, but each differentRF channels may go to different WCMs 34. Many WCMs 34 can share a singleor multiple downstream RF channels 30. Data is transmitted via the RFchannels 30 by framing DOCSIS MAC frames into Motion Picture ExpertsGroup—Transport Stream (MPEG-TS) packets.

The WCMs 34 can simultaneously demodulate each of the different channels30 and regenerate the different portions of the original data streamreceived on link 27. In one example, the different portions of the datastream distributed over the different downstream RF channels 30 arereformatted back into Ethernet frames and sent over link 36 to an IP SetTop Box (STB) 38. The STB 38 converts the digital data contained in theEthernet frames into an analog signal for displaying on a television 40.

FIG. 3 shows the circuitry in the WCMTS 28 and the WCM 34 that encodeand decode the wideband channel 35. The WCMTS 28 includes a backplane 42that couples data from the WAN connection 27 to a wideband transmitframer 44 and a Media Access Control (MAC) interface 46. In oneembodiment, the wideband framer 44 separates Ethernet frames intowideband packets that are transmitted simultaneously over the multipledownstream channels 30.

In one example, the wideband channels 30 are each modulated usingQuadrature Amplitude Modulation (QAM). In one example, 64 QAM modulationwith 16 downstream RF channels 30 provides approximately 480 Millionbits per second (Mbps) of downstream bandwidth. Using 256 QAM modulationprovides approximately 640 Mbps of downstream bandwidth. Each downstreamRF channel 30 is associated with a Quadrature Amplitude Modulator (QAM)and Up-Converter (U) 48. The Q&U's 48 each modulate the MPEG digitaldata over a different RF channel.

The MAC interface 46 is also used for transmitting DOCSIS IP data over asingle RF channel 30A and receiving DOCSIS IP data over upstream RFchannel 32. A demodulator 50 demodulates upstream IP traffic receivedover upstream channel 32. The MAC 46 in the WCMTS 28 can use the sameQ&U 48A for transmitting narrowband traffic, wideband traffic, or bothnarrowband and wideband traffic over downstream channel 30A.

Each WCM 34 includes a wideband tuner 54 that includes multiple Tuners(T) and QAM demodulators (D) 56. The T&Ds 56 demodulate the digital datafrom the downstream channels 30. A wideband Receive (Rx) framer 58reassembles data received over the different RF channels 30 into thedata stream originally sent by the server 26 (FIG. 2).

A decoder 60 includes a DOCSIS MAC/PHY interface for controlling howMPEG frames are reassembled into Ethernet frames and sent over theEthernet link 36. The MAC/PHY interface is also used for sending IP dataover upstream RF channel 32 to the MAC interface 46 in CMTS 14. The MACinterface 46 in the WCMTS 28 sends a Wideband Channel Descriptor (WCD)55 to the WCMs 34 that indicate which RF channels 30 are part of thewideband channel 35.

Wideband Formatting

FIG. 4 shows vertical striping of wideband MPEG-TS packets 69 in a4-wide wideband channel 35. Wideband MPEG-TS packets 69 carry widebandDOCSIS data.

Vertical Alignment Indexes (VAIs) increment across the horizontalMPEG-TS packets 69. The VAI values in a vertical group of widebandMPEG-TS packets are shown on the horizontal axis. For example, thewideband MPEG-TS packets 1-4 are assigned VAI values of 0.

The wideband channels are effectively independent of the layer-1physical layer (PHY) and operates as a shim between the PHY layer andthe layer-2 MAC layer. This allows the downstream bandwidth to benoncontiguous. The bandwidth assigned to a particular WCM can bedistributed in different noncontiguous portions of the total availableRF spectrum. In other words, any selectable combination ofnon-contiguous RF channels can be used for any wideband channel.

The VAIs indicate a time sequence for the wideband MPEG-TS packets 69transmitted over the RF channels. The WCMs 34 use the VAIs to realignthe wideband MPEG-TS packets 69 received from the WCMTS 28 over thedifferent RF channels. A Radio Frequency (RF) table (FIG. 17) identifiesthe frequencies for the RF channels and the order that the identified RFchannels should be decoded by the WCM 34.

The decoder 60 uses the VAI's to temporally align the wideband MPEG-TSpackets 69 transmitted over the multiple RF channels. The decoder 60then decodes particular RF channels in a particular channel sequenceidentified in the RF table (FIG. 17).

In the example shown in FIG. 4, the decoder 60 reads the widebandMPEG-TS packet 1 in RF channel 1 and then reads the wideband MPEG-TSpacket 2 in RF channel 2. The decoder 60 combines other wideband packets3, 4, 5, etc. from the RF channels in a similar manner. Different WCMs34 could scan different RF channel frequencies and in different RFchannel orders according to the sequence of frequencies contained in theRF table.

FIG. 5 shows the format of the wideband MPEG-TS packet 69 in moredetail. The wideband packet 69 consists of a MPEG-TS header 70, apointer_field 72 (may not be present in all wideband packets), awideband header 74, and a DOCSIS payload 76. One example of fieldscontained in the standard MPEG-TS header 70 shown in Table 1.0.

A Packet Identifier (PID) exists in the current MPEG transport scheme.Particular PID values are used in a novel manner in one embodiment ofthe present invention to identify payloads associated with widebandchannels. The wideband PID values are used along with the RF table bythe WCMs 34 (FIG. 2) to decode wideband payloads that extend overmultiple downstream channels.

A Continuity Counter (CC) is a prexisting field used in a conventionalMPEG header. The CC is used in a novel manner in one embodiment of thepresent invention for tracking wideband MPEG-TS packets that extend overmultiple RF channels.

The pointer_field 72 contains the number of bytes in the wideband packet69 that immediately follow the pointer_field 72 that the framer 58 (FIG.3) in the WCM 34 must skip before looking for the beginning of a DOCSISMAC frame. The pointer_field 72 may point to the beginning of a DOCSISMAC frame. Alternatively, the pointer_field 72 may point to any stuffbyte preceding the DOCSIS MAC frame. The pointer_field was previouslyused in DOCSIS to identify consecutive MPEG-TS packets in a same RFchannel. The wideband scheme according to one embodiment of theinvention uses the pointer_field 72 to identify payloads that extendacross multiple RF channels.

TABLE 1.0 MPEG-TS Header Format for Wideband MPEG-TS packets LengthField (bits) Description sync_byte 8 MPEG-TS packet Sync bytetransport_error_indicator 1 Indicates an error has occurred in thereception of the packet. This bit is reset to zero by the sender, andset to one by the receiver whenever an error occurs in transmission ofthe packet. payload_unit_start_indicator 1 A value of one indicates the(PUSI) presence of a pointer_field as the fifth byte of the packettransport_priority 1 Reserved; set to zero PID 13 Wideband channelpacket identifier: transport_scrambling_control 2 Reservedadaptation_field_control 2 Use of the adaptation_field may not beallowed on wideband channel PIDs continuity_counter (CC) 4 Cycliccounter within a wideband channel PID per RF channel

Table 2.0 shows the wideband header 74 in more detail. The widebandheader 74 contains reserved bits followed by the Vertical AlignmentIndex (VAI). The reserved field can be used to compensate for skew. Forexample, one of the RF channels may be substantially ahead of the otherRF channels. The reserved field may be used to identify the same VAI fortwo sequencial wideband MPEG-TS packets. The exact position of thewideband header 74 within a wideband MPEG-TS packet 69 can varydepending on whether or not the pointer_field 72 is present.

TABLE 2.0 Wideband Header Format Length Field (bits) DescriptionReserved 2 Reserved Vertical Alignment 6 A cyclic counter generated bythe Index WCMTS conveys the vertical alignment of wideband MPEG-TSpackets on all associated RF channels.

The DOCSIS payload 76 in wideband MPEG-TS packet 69 can carry DOCSIS MACframes and can also carry stuff bytes. The WCMTS 28 can insertconventional MPEG-TS null packets or wideband MPEG-TS null packets in aninactive wideband channel. Unlike conventional MPEG-TS null packets,wideband MPEG-TS null packets can provide VAIs to the WCMs 34.

The DOCSIS MAC frames can begin anywhere within the payload 76 of thewideband MPEG-TS packet 69 and may span multiple wideband MPEG-TSpackets. Several DOCSIS MAC frames may exist within a single widebandMPEG-TS packet.

FIG. 6 shows a Payload Unit Start Indicator (PUSI) bit in the MPEG-TSheader 70 that indicates the presence or absence of the pointer_field 72as the first byte of the MPEG-TS payload. The start of a DOCSIS MACframe 78 in DOCSIS payload 76 is positioned immediately after thewideband header 74. In FIG. 6, the pointer_field 72 is 1, and thedecoder 60 in the WCM 34 begins searching for a valid DOCSIS MACsublayer Frame Control (FC) immediately following the wideband header74.

FIG. 7 shows the case where a DOCSIS MAC frame 2 is preceded by the tailof a previous DOCSIS MAC frame 1 and possibly a sequence of stuff bytes83. The pointer_field 72 identifies the first byte after the tail offrame 1 (which could be a stuff byte) as the position where the decoder60 in the WCM 34 should begin searching for a DOCSIS MAC sublayer framecontrol value.

FIG. 8 shows multiple DOCSIS MAC frames 1, 2, and 3 contained within thesame wideband MPEG-TS packet 69. The DOCSIS MAC frames may follow oneafter the other, or may be separated by an optional sequence of stuffbytes 83. FIG. 9 shows the case where, a DOCSIS MAC frame 1 spansmultiple wideband MPEG-TS packets 69A, 69B and 69C. The wideband MPEG-TSpacket 69C encapsulates the start of the next MAC frame 2. Thepointer_field 72C for wideband packet 69C points to the byte followingthe last byte of the tail of MAC frame 1.

Wideband Dynamic Bandwidth Allocation

FIG. 10 shows how the bandwidth of the wideband channel can bedynamically adjusted by changing the number of RF channels. In oneexample, the wideband channel bandwidth is adjusted at wideband MPEG-TSpacket boundaries. The WCMTS 28 (FIG. 3) can dynamically vary thebandwidth of multiple different wideband channels simply by varying thewideband configuration parameters in the RF table associated withdifferent PIDs.

For example, FIG. 10 shows three wideband channels PID=X, Y, and Zmapped over four RF channels 1-4. The three wideband channels areconfigured using a RF channel frequency tables. The RF channel frequencytable is part of the wideband channel descriptors that specify widebandchannels as entering over RF channels 1-4. The channel frequency tableis part of the wideband channel descriptor 55 shown in FIG. 17.

Pursuant to the RF frequency table, the WCM 34 finds the wideband databy monitoring all four RF channels 1-4 for wideband packets havingcertain PID values (See Table 1.0). The WCM 34 further filters thewideband channel data by, looking for MAC addresses in the DestinationAddress (DA) field of the Ethernet packets in the DOCSIS MAC framepayloads within the wideband channel.

FIG. 10 shows a wideband channel PID=X that uses the entire bandwidth ofall four RF channels 1, 2, 3, and 4 when the wideband MPEG-TS packets 69have Vertical Alignment Indexes (VAI) equal to N. For the next widebandMPEG-TS packets transported at VAI=N+1, RF channels 1 and 2 carrywideband channel PID=Y and RF channels 3 and 4 continue to carrywideband channel PID=X. The equal division of bandwidth between widebandchannels X and Y continues until the wideband MPEG-TS packets have VAIsequal to M+1.

At VAI=M+1, wideband channel X again utilizes the entire bandwidth ofall four RF channels. This RF channel utilization continues up to andincluding when the transported wideband MPEG-TS packets have VAIs equalto P. When the next wideband MPEG-TS packets are transported at VAI=P+1,RF channels 2-4 are used for wideband channel Z while RF channel 1 isused for wideband channel X.

The WCM decoder 60 reads the PID values in each wideband packet 69.Since all wideband packets for VAI=N have the same PID value, the WCMdecoder 60 combines these packets together as part of the same widebandchannel. At VAI=N+1, the wideband packets for RF channels 1 and 2 havePID=Y and the RF channels 3 and 4 have PID=X. The WCM decoder 60 byreading the PIDs knows to combine the MPEG frames, if appropriate, forwideband channel X in the RF channels 3 and 4 with other MPEG framespreviously received in RF channels 1-4 for wideband channel X at VAI=1.The WCM decoder 60 similarly combines when appropriate the MPEG framesreceived in wideband channel Y over RF channels 1 and 2 for VAI=N+1through VAI=M.

FIG. 11 shows how the Vertical Alignment Indexes (VAIs) operate incombination with Continuity Counters (CCs). The CC is a fieldincremented with each transport stream packet having the same PacketIdentifier (PID). In one example, seventeen wideband MPEG-TS packetslots VAI=0 through VAI=16 are transmitted over each of four RFchannels. Two wideband channels X and Y are mapped over the four RFchannels 1, 2, 3 and 4.

The VAI values are used for aligning vertical groups of wideband MPEG-TSpackets across all the RF channels. The CC values increment horizontallyacross RF channels according to the wideband channel. The CCs inwideband MPEG-TS packets are treated independently for each RF channelPID. This allows the WCM decoder 60 to determine which wideband packetsin a sequence for a particular RF channel have been received, even whenwideband packets for a particular wideband channel are not transmittedfor certain VAI packet slots.

FIG. 12 shows six fiber nodes A-F, each with a separate forward carrierpath. Each forward carrier path contains its own RF spectrum. Thewideband channels WB1-WB4 are associated with the RF channels 1-4 andthe narrow band channels NB1-NB4 are associated with RF channel 5. Fibernodes A and 13 each share the same narrowband channel NB 1 and widebandchannel WB 1. This results in a single association of WB 1 to NB 1. Itshould be understood that this is only one example, and any combinationof any number of wideband and narrowband channels can be associated withany number and combination of RF channels.

Fiber nodes C and D share wideband channel WB2 and each have their ownnarrowband channels NB2 and NB3, respectively. This results in twoseparate associations of WB2 to NB2, and WB2 to NB3. Fiber nodes E and Fshare the same narrowband channel NB4, but have different widebandchannels WB3 and WB4, respectively. This results in two separateassociations of WB3 to NB4 and WB4 to NB4. In one embodiment, there isone PID associated with each wideband channel. The wideband channeldescriptors associated with a particular PID then identify to the WCMsof the RF channels and sequence associated with the wideband channelsand narrowband channels.

The wideband channel descriptor 55 (FIG. 3) is sent by the WCMTS 28 overthe narrowband channel 30A. The WCD 55 contains channel descriptors thatidentify the RF channel frequencies, sequence, and PIDs for the widebandchannels associated with each fiber node A-F. Each unique association ofwideband channel to narrowband channel may have its own wideband channeldescriptor.

Interleaving Wideband and Narrowband Channels

Narrowband and wideband cable modems can receive narrowband MPEG-TSpackets over either an RF channel dedicated to a narrowband channel, oran RF channel where wideband and narrowband channels are interleaved.FIGS. 13 and 14 illustrate two different scenarios.

FIG. 13 shows five RF channels 1-5. RF channels 1-4 carry widebandMPEG-TS packets 90 for wideband channel X. The RF channel 5 carriesnarrowband MPEG-TS packets 92 in a narrowband channel (PID=DOCSIS PID).The wideband packets 90 from RF channels 1-4 are combined together bythe WCM 34 to generate a single wideband data stream. The narrowbandpackets 92 from RF channel 5 are combined together to generated a singlenarrowband data stream.

FIG. 14 shows another interleaving configuration where RF channels 1-4carry both wideband and narrowband channels. The wideband channel Xextends over different combinations of all four RF channels 1-4 and thenarrowband channel (PID=DOCSIS PID) is interleaved with the widebandchannel X on RF channel 4.

The bandwidth of wideband channel X can be dynamically adjusted to allowthe narrowband channel 92 to share the bandwidth of RF channel 4 duringthe packet slots from VAI=N+1 through VAI=M. The WCMs 34 (FIG. 3) areconfigured using the WCD 55 (FIG. 17) to receive wideband channel X overRF channels 1-4. The WCM decoder 60 identifies the narrowband packet 92at VAI=N+1 by detecting PID=DOCSIS PID in the MPEG-TS header. The WCMdecoder 60 processes the narrowband packet 92 as a conventional singleband DOCSIS MPEG-TS packet by combining packet 92 with other narrowbandpackets identified (PID=DOCSIS PID) on RF channel 4.

FIG. 15 is an example showing how DOCSIS MAC frames span multiplewideband MPEG-TS packets 98 even when the wideband channel bandwidthdynamically changes. In this example, two wideband channels PID=X andPID=Y and a narrowband channel 94 are interleaved across four RFchannels 1-4. The wideband channel descriptor in FIG. 17 identifies theRF channels 1-4 associated with wideband channels X and Y.

The first three wideband MPEG-TS packets transmitted on RF channels 1-3have VAI=0 and PID=X. The RF channel 4 at VAI=0 has a PID=DOCSIS PID. AtVAI=1, RF channels 1 and 2 have PID'=Y. The wideband MPEG-TS packets forRF channels 3 and 4 at VAI=1 have PID=X. Narrowband MPEG-TS packets donot contain a VAI field. The values of the Continuity Counters (CCs) inthe first four vertical MPEG-TS packets are arbitrarily chosen toillustrate the independence of CCs between RF channels.

The decoders 60 in the WCMs 34 conduct the following wideband stripingsequence according to the above VAI and PID values. The DOCSIS MAC frameX1 begins inside the wideband MPEG-TS packet 98 with VAI=0 on RF channel1. The PID value of X in the MPEG-TS header 96 identifies the widebandMPEG-TS packet 98 as part of wideband channel X. The wideband MPEG-TSpacket 98 has a Payload Unit Start Indicator (PUSI) bit in the MPEG-TSheader 96 set to 1, indicating that the pointer_field is present. Thepointer_field points to one of the stuff bytes 97 preceding thebeginning of DOCSIS MAC frame X1.

The DOCSIS MAC frame X1 continues in the wideband MPEG-TS packet 100 onRF channel 2 at VAI=0. The entire payload of the wideband MPEG-TS packet100 contains the continuation of DOCSIS MAC frame X1 from RF channel 1.The PUSI bit is accordingly set to 0 and there is no pointer_field. Inone embodiment, stuff bytes are only inserted between DOCSIS MAC frames,therefore no stuff bytes exist in wideband MPEG-TS packet 100.

The DOCSIS MAC frame X1 ends on the wideband MPEG-TS packet 102 on RFchannel 3 at VAI=0. The DOCSIS MAC frame X1 is immediately followed byDOCSIS MAC frame X2. The DOCSIS MAC frame X2 is a small frame totallycontained in wideband MPEG-TS packet 102. The pointer_field 106 is usedin wideband packet 102 to point to the beginning of new DOCSIS MAC frameX2. The DOCSIS MAC frame X2 is followed by optional stuff bytes 108 andthe beginning of DOCSIS MAC frame X3.

Although wideband MPEG-TS packet 102 contains the beginning of twoDOCSIS MAC frames X2 and X3, the pointer_field points to the first newMAC frame X2.

The narrowband MPEG-TS packet on RF channel 4 and the wideband MPEG-TSpackets with VAI=1 on RF channels 1 and 2 do not have a PID value of X.The DOCSIS MAC frame X3 accordingly is continued on the next widebandMPEG-TS packet 104 with VAI=1 and PID=X on RF channel 3. The DOCSIS MACframe X3 ends in the wideband MPEG-TS packet 110 on RF channel 4 havingVAI=1. The DOCSIS MAC frame X3 in wideband packet 110 is followed by anumber of stuff bytes 114 and the start of DOCSIS MAC frame X4. Thepointer_field 112 in wideband MPEG-TS packet 110 points to the beginningof DOCSIS MAC frame X4. Alternatively, the pointer_field 112 could pointto any of the preceding stuff bytes 114.

MPEG Over MPEG Byte Striping

FIG. 16 shows one alternative embodiment referred to as vertical bytestriping. Referring to FIGS. 3 and 16, a wideband transport channel 120is created by vertically byte-striping MPEG-TS packets over multiplehorizontal MPEG-TS streams. At the physical layer, each RF channel 1-4runs independently as a separate MPEG-TS stream. At the link layer, thewideband transmitter 44 aligns the various RF channels 1-4 that make upa wideband transport sub-channel by selecting values in the PID field inMPEG-TS header 125. The wideband decoder 60 in FIG. 3 corrects forjitter in the RF channels 1-4 between the wideband transmitter 44 andwideband receiver 58 using the VAI values 124 to realign the horizontalMPEG-TS streams. The receiving WCMs 34 recreate the original MPEG-TSstream by de-striping the vertical MPEG-TS stream from the horizontalMPEG-TS streams.

The wideband channel 120 can be run as a single fat wideband transportsub-channel, sub-divided into several smaller wideband transportsub-channels, or run as a mixture of wideband transport sub-channels andnarrowband channels. In FIG. 16, during the first horizontal MPEG-TSpacket time, RF channels 1, 2 and 3 are run as a 3-wide widebandtransport channel, while RE channel 4 is run as a narrowband channel.

The PID field in the MPEG packet header 125 indicates which RF channelsare being used to stripe the wideband data for a given widebandtransport sub-channel. The PID is set to the value of X for the widebandtransport sub-channel. The PID value X can be any value except reservedvalues (e.g. 0x1FFFE). In this example, the WCMTS 28 knows that there isa 4-channel wide wideband receiver 58 listening on the four RF channels1-4.

The WCMTS 28 may decide that it needs to use three of the four RFchannels to keep up with Quality of Service (QoS) bandwidthrequirements. Accordingly, the WCMTS 28 transmits with the PID set to Xover RF channels 1, 2, and 3. During the next MPEG-TS packet time, theWCMTS 28 may decide that it only needs two RF channels worth ofbandwidth and transmits with a PID set to X only over RF channels 3 and4.

The WCM 34 looks on the four RF channels 1-4 for wideband channels witha PID=X and de-stripes the wideband data from all MPEG-TS packets havinga PID=X. If another wideband channel PID value is detected, the WCM 34combines that wideband packet with other wideband packets having asimilar PID value.

This dynamic channel assignment allows the WCMTS 28 to balance the loadbetween all the subscribers by simply choosing which and how many RFchannels to stripe the wideband transport sub-channel for any given timeslot. The WCMTS 28 does not need to notify the WCM a priori, as the PIDinformation is sent in-band and is sufficient for the WCM 34 to adjustthe received channels dynamically to keep up with the WCMTStransmission.

Wideband Channel Descriptor (WCD)

FIGS. 17 and 18 show how a Wideband Channel Descriptor (WCD) 55 istransmitted by a wideband capable CMTS 28 at periodic intervals todefine the characteristics of a logical wideband downstream channel. Aseparate message may be transmitted for each logical wideband downstreamchannel that is currently available for use. The CMTS 28 generates WCDs55 that contain the information shown in FIG. 17.

A configuration change count is incremented by one by the CMTS 28whenever any of the values of the channel descriptors in WCD 55 change.If the value of the count in a subsequent WCD 55 remains the same, theWCMs 34 can quickly decide that the channel operating parameters havenot changed, and may be able to disregard the remainder of the message.

The WCD 55 includes a MAC management header 130, a transaction ID 132and TLVs 134 containing wideband configuration data 134 that specifieshow PID 136 is used in the wideband packet header to identify thewideband channel. The TLVs 134 specifies in field 140 the number ofphysical RF channels used to carry the wideband channel and identifiesin field 138 narrowband downstream channels associated with the widebandchannel.

The TLVs 134 can include the RF table 142 that contains a sequencenumber 144 indicating what order the RF channel payloads are decoded bythe WCMs. Center frequencies 146 indicate the frequences for each RFchannel used in the wideband channel. The RF channels may be sequencedin any order and may or may not be adjacent in frequency to each other.

The WCMTS 28 and WCM 34 can support data link encryption within thewideband channels. The WCMTS 28 may or may not use the same encryptionand keying for the WCM 34 used on the associated narrowband channel. Thecable modems can accept the same keying on both the narrowband channeland with wideband channel, or can accept separate keying for widebandand narrowband channels.

Wideband Channel Acquisition

FIG. 18 shows how the WCM 34 acquires a logical wideband channel. TheWCM 34 first acquires a DOCSIS narrowband channel 130A and completesranging making an upstream channel 132 operational. The WCMTS 28 assignsa PID value to the WCM 34 and downloads the WCD 55 containing thewideband channel parameters including the frequency table 142 to the WCM34.

The WCM 34 reads the wideband channel descriptors 55 having the assignedPID 136 (FIG. 17). The WCM 34 issues a REG-REQ 134 to the WCMTS 28 alongwith any WCD wideband capabilities parameters 136. After the WCM 34receives an REG-RSP 138 back from the WCMTS 28, all downstream RFchannels 130A-130N are acquired that are identified as comprising thewideband channel. A REG-ACK 140 is sent from the WCM 34 back to theWCMTS 28. The WCM 34 then starts receiving data on the assigned widebandPID.

The WCMTS 28 can periodically reassign different wideband perameters toone or more of the wideband cable modems 34. For example, the WCMTS 28may send a wideband channel descriptor 55 to a WCM 34 lists a first setof RF channels in a first sequence for the WCM's wideband channel. Sometime later, the WCMTS 28 may send another wideband channel desciptor 55having the same associated PID value but that contains a different setof RF channels to be used as wideband or narrowband channels or thatlists the same set of RF channels in a different order.

The WCMTS 28 can use the wideband channel descriptors 55 to dynamicallysend different wideband configuration data to particular WCMs 34 basedon changing bandwidth requirements. For example, at different timesthere can be different wideband and narrowband payload demands. TheWCMTS 28 uses the wideband channel descriptor 55 to dynamically reassignthe RF channels to different wideband and narrowband channels accordingto these changing bandwidth demands.

The dynamic assignment of RF channels can also be used to increasesystem reliability. For example, the WCMTS or WCM may identify faults inone or more RF channels. The WCMTS can then send a wideband channeldescriptor 55 containing a new RF table to the WCMs using the RFchannels identified with faults. The new RF table dynamically drops theidentifed RF channels from the wideband or narrowband channels.

A CM without wideband capabilities may not recognize any of the newwideband-specific TLVs 134 in the WCD 55. The CM may be unable toregister successfully if provisioned with the WCD 55 that containswideband-specific parameters. When interoperating with a CM that doesnot have wideband-specific capabilities, the WCMTS 28 would allow a CMto register and operate as a CM. When WCM 34 registers with the WCMTS28, the WCMTS 28 may return the REG-RESP message 138 that configures theWCM 34 in a mode with or without wideband-specific capabilities.

When interoperating with a WCMTS 28, a CM without wideband-specificcapabilities receives data on a single RF channel 130A. Wheninteroperating with a CMTS without wideband-specific capabilities, a WCM34 receives data on a single RF channel 130A.

Packet Skew

Wideband MPEG-TS packet skew is defined to be the maximum expected skewfrom the arrival of the first MPEG-TS packet with a given VAI to thearrival of the last MPEG-TS packet with the same VAI within a givenwideband channel. The skew is measured at the WCM receiver MAC interfaceto the PHY.

The MPEG-TS packets that make up a wideband channel are de-skewed usingthe VAI in the wideband MPEG header 74 (FIGS. 6-9). The MPEG-TS packetswith PID values other than those defined to be wideband PIDs, includingnarrowband packets (PID=DOCSIS PID) and MPEG-TS nulls, will not containvalid VAIs. If the WCM 34 does not receive an MPEG-TS packet for a givenVAI within the specified maximum skew window for any given RF channel ofthe wideband channel, the WCM 34 concludes no wideband MPEG-TS packetwas sent on that RF channel for the given VAI.

Alternatively, the next consecutive CC for that PID may be received inanother VAI packet slot. The WCM 34 may then conclude that no widebandpacket for that PID was sent in the previous VAI packet slot.

The system described above can use dedicated processor systems, microcontrollers, programmable logic devices, or microprocessors that performsome or all of the operations. Some of the operations described abovemay be implemented in software and other operations may be implementedin hardware.

For the sake of convenience, the operations are described as variousinterconnected functional blocks or distinct software modules. This isnot necessary, however, and there may be cases where these functionalblocks or modules are equivalently aggregated into a single logicdevice, program or operation with unclear boundaries. In any event, thefunctional blocks and software modules or features of the flexibleinterface can be implemented by themselves, or in combination with otheroperations in either hardware or software.

Having described and illustrated the principles of the invention in apreferred embodiment thereof, it should be apparent that the inventionmay be modified in arrangement and detail without departing from suchprinciples. I claim all modifications and variation coming within thespirit and scope of the following claims.

1. An apparatus, comprising: a wideband cable modem configured toreceive and decode a logical wideband channel received over a pluralityof downstream Quadrature Amplitude Modulation (QAM) channels, whereinthe logical wideband channel spans across a first combination of some ofthe QAM channels at a first time and a second different combination ofsome of the QAM channels at a second later time; and the wideband cablemodem configured to monitor all the QAM channels for packets having aparticular packet identifier value that correlates said packets to thelogical wideband channel, to track dynamic utilization of the QAMchannels by the logical wideband channel over the different timesaccording to the monitoring; wherein the correlated packets includeVertical Alignment Indexes (VAIs) to identify temporal positions of saidpackets in the plurality of QAM channels, and wherein the wideband cablemodem is configured to use the VAIs to temporally realign the packetsreceived over the different QAM channels.
 2. The apparatus of claim 1,wherein the wideband cable modem is configured to inspect Moving PictureExperts Group (MPEG) Packet IDentifier (PID) fields for the particularpacket identifier value to distinguish the packets of the logicalwideband channel from other packets received over the QAM channels. 3.The apparatus of claim 1, wherein ones of the packets associated with afirst transmit time have a same VAI value that is different than a VAIvalue of those ones of the packets associated with a second differenttransmit time.
 4. The apparatus of claim 1, wherein the wideband cablemodem includes a plurality of tuners having demodulators each configuredto demodulate a different one of the QAM channels.
 5. The apparatus ofclaim 1, wherein the wideband cable modem is configured to identify theQAM channels according to a received wideband channel descriptor.
 6. Theapparatus of claim 1, wherein the wideband cable modem is configured touse the same QAM channels for decoding both the logical wideband channeland a narrowband channel.
 7. The apparatus of claim 1, wherein thereceived packets have an MPEG header, a wideband header and a Data OverCable Service Interface Specification (DOCSIS) payload that containsMedia Access Control (MAC) frames.
 8. The apparatus of claim 1, whereinthe wideband cable modem is configured to inspect continuity values tothe packets that identify an order that the packets are transmitted overthe different QAM channels.
 9. A method, comprising: receiving anddecoding a logical wideband channel received over a plurality ofdownstream channels, wherein the logical wideband channel spans across afirst combination of some of the downstream channels at a first time anda second different combination of some of the downstream channels at asecond later time; and monitoring all the downstream channels forpackets having a particular packet identifier value that correlates saidpackets to the logical wideband channel, to track dynamic utilization ofthe downstream channels by the logical wideband channel over thedifferent times according to the monitoring; wherein the correlatedpackets include Vertical Alignment Indexes (VAIs) to identify temporalpositions of said packets in the plurality of downstream channels, andwherein the method further comprises using the VAIs to temporallyrealign the packets received over the different downstream channels. 10.The method of claim 9, further comprising inspecting Moving PictureExperts Group (MPEG) Packet IDentifier (PID) fields for the particularpacket identifier value to distinguish the packets of the logicalwideband channel from other packets received over the downstreamchannels.
 11. The method of claim 9, wherein ones of the packetsassociated with a first transmit time have a same VAI value that isdifferent than a VAI value of those ones of the packets associated witha second different transmit time.
 12. The method of claim 9, furthercomprising demodulating the downstream channels using a plurality oftuners.
 13. The method of claim 9, further comprising identifying thedownstream channels according to a received wideband channel descriptor.14. The method of claim 9, further comprising using the same downstreamchannels for decoding both the logical wideband channel and a narrowbandchannel.
 15. The method of claim 9, wherein the received packets have anMPEG header, a wideband header and a Data Over Cable Service InterfaceSpecification (DOCSIS) payload that contains Media Access Control (MAC)frames.
 16. The method of claim 9, further comprising inspectingcontinuity values to the packets that identify an order that the packetsare transmitted over the different downstream channels.
 17. An articleof manufacture including a tangible computer-readable medium havinginstructions stored thereon that, in response to execution by acomputing device, cause the computing device to perform operationscomprising: receiving and decoding a logical wideband channel receivedover a plurality of downstream channels, wherein the logical widebandchannel spans across a first combination of some of the downstreamchannels at a first time and a second different combination of some ofthe downstream channels at a second later time; and monitoring all thedownstream channels for packets having a particular packet identifiervalue that correlates said packets to the logical wideband channel, totrack dynamic utilization of the downstream channels by the logicalwideband channel over the different times according to the monitoring;wherein the correlated packets include Vertical Alignment Indexes (VAIs)to identify temporal positions of said packets in the plurality ofdownstream channels, and wherein the operations further comprise usingthe VAIs to temporally realign the packets received over the differentdownstream channels.
 18. The article of manufacture of claim 17, whereinthe operations include inspecting Moving Picture Experts Group (MPEG)Packet IDentifier (PID) fields for the particular packet identifiervalue to distinguish the packets of the logical wideband channel fromother packets received over the downstream channels.
 19. The article ofmanufacture of claim 17, wherein the operations include demodulating thedownstream channels using a plurality of tuners.
 20. The article ofmanufacture of claim 17, wherein the operations include inspectingcontinuity values to the packets that identify an order that the packetsare transmitted over the different downstream channels.